Sensitizing in color photography



smusnxzme mcomn PHOTOGRAPHY Filed March 4, 1943 I BLUE SENSITIVE EMULSION WITH MINOI? AMOUNT OF RED SENSITIVITY N-JF YELLOW FILTER LAYER a p GREEN SENSITIVE EMULSION RED SENSITIVE EMULSION SUPPORT v RALPH M. EVANS WESLEY T. HANSON, JR.

INVENTORS ATTORNEYS more particularly to. a method color sensitizing in color photography.

red sensitivity is 40 to $400 of the Patented Oct. 10,1944

Ralph M. Evans and Wesley T.

minors to Eastman Kodak Company, Rochester, N. Y.

ester N. Y.,

. Jersey Hanson, Jr., Rocha corporation or New Application March 4, 1943, Serial No. 417,904

photography and of improving the This invention relates to color The first requirement of a multi-color process is that the gray scale be balanced-that is, that the neutrals be reproduced as plish this result, the dyes or neutral. 1 To accominks employed in the picture or print must be balanced so that a gray scale can be reproduced, including the reproduc tion of white as white.-

It is well known that when equal amounts of the yellow and magenta dyes or.- lnks available for,

the subtractive method mixed, an orange is the Thus, when the gray scale is balanced, the image produced from'a red is actually orange, and not It is, therefore. the principal object of this invention to provide a method for improvement of the color rendition in a subtractive color procsea.- A further object is to provide a method for of color photograph are improving'the reproduction of colors which have a yellow component.

These objects are accomplished in a color process employing elements sensitive to the blue, reen, and red spectral regions, by sensitivity of the blue-sensitive element into the red region of the spectrum so that the effective blue sensitivity.

In the accompanying drawing, the single figure is a sectional view of a multi-layer material sensitised according to our invention.

In carrying out our invention, a blue-sensitive photographic emulsion, of the gelatino-silver bromide or bromoiodide type is sensitized to red light y mixing with it an optical sensitizing dye producing such sensitivity. The emulsion is then coated, either aspart of a multi-layer material with green sensitiveand red-sensitive emulsion layers-or on a separate support for the preparation of separation images.

A suitable material is illustrated in the accompanying drawing, in which a support It is coated with emulsion layers It and I2, sensitive, respectively, to the red and green regions of the spectrum,.and a yellow filter layer l3 over layer I 2. The outer layer It is a blue-sensitive emulsion layer which has a conferred sensitivity in the red region in the amount of about ,40 to, Moo of its v blue sensitivity.

In the preparation of the emulsions according to our invention, we prefer to use a red sensitizer which confers little or no green sensitivity, although sensitizing in both the green and the red regions can be employed. The sensitizing is preresult rather than a red.

extending the '5 Claims. 21. 95-2) i'erably such that images of the same contrast are produced by exposure to red light and to blue light, although the sensitizing may be such that the contrast when exposed by light other than blue, is much lower than the contrast produced by blue ight.

Our invention will not be described by reference to the followingv examples, which are illustrative only.

E's-ample 1 To 1000 grams of a fine-grain gelatino-silver the emulsion. This light and containing about 40 grams of silver bromide there was added 0.4 mg. of 2.2'-diethyl- 5,6,526' dibenzoxadicarbocyanine, with stirring- This produced an emulsion sensitive to blue and red light without any appreciable green sensitivity. The red light sensitivity was approximately te of the blue light sensitivity. The emulsion was coated as the top layer of a multi-layer element.

Example 2 To 1000 grams of a gelatino-silver' bromide emulsion similar-to that of Example 1 there was added 0.6 mg. 01" 2,2'-diethylthia-4'-dicarbocyanine iodide, with stirring. This produced an emulsion having blue and red sensitivity with no appreciable green sensitivity. The emulsion was coated as in Example 1.

In Examples 1 and 2 the contrast of the emulsion to red light was substantially the same as the contrast to blue'light. In the following example,

7 the contrast to red light is much lower than the contrast to blue light.

1000 grams of a fine-grain; silver bromide negative emulsion sensitive only to blue light was divided into two portions of approximately 250 grams and 750 grams. The 250 gram portion was sensitized to red light with 0.75 to 1.25 mgs. of,

,6'-dibenzthiacarbocyanine bro- 3,3'-diethyl-5,6,5' mide. This portion of theemulsion was held for about 10 minutes a 45 to 50 C., and was then mixed with the remaining 750 gram portion of produces an emulsion having much less red sensitivity than blue sensitivity, and also lower contrast when exposed to red light than when exposed to blue light.

Upon exposure of a as that described in Example 1, the top emulsion layer records the blue light of the image, and also records some of the red light, if any red light is Present. The red multi-layer lement such component is recorded in the bottom emulsion layer in the usual way, but, in addition, some red light is recorded in the top emulsion layer. If a positive red component image is produced in the bottom layer, a positive image representing part of the red light is also produced in the top layer, rather than a negative as in the case of masking. Loss of yellow dye in the top'layer is, therefore, brought about, and in order to maintain the neutrals oi the image, tlie sensitivity of the top layer to blue light must be decreased by an amount equal to the red sensitivity of that layer. This is usually an easy matter; since the red-sensitivity-is verylow when compared with the blue sensitivity.

The result of the minor amount of red sensimatic improvement of the reds in the picture. Reds are brighter and less orange than they are with the usual sensitizing.

which comprises sensitizing the blue-sensitive layer to red light in an amount approximately ho to /100 of its blue light sensitivity.

2. The method of improving the color rendition of a multi-layer photographic material havin superposed red-, green-, and blue-sensitive gelatino-silver halide emulsion layers, in which subtractive dye images are formed, the combination of yellow and magenta in equal amounts being too orange, which comprises sensitizing the bluesensitive silver halide layer to red light in an is tivity in the blue-sensitive emulsion is an autoamount approximately [10 to lino of its blue light sensitivity.

3. The method'of improving color reproductionin a three-color photographic process employing gelatino-silver halide emulsion layers separately sensitive to the red, green, and blue spectral regions, in which subtractive dye images are formed, the combination of yellow and magenta in equal amounts being too orange, which comprises extending the sensitivity of the blue-sensitive emulsion into the red spectral region by an amount from /10 to of the blue light sensitivity of that emulsion, and recording insaid emulsion the blue component and that amount of the red component by which the layer is sensitive to red light.

4. A multi-layer photographic element comprising superposed gelatino-silver halide emulsion layers separately sensitive to the red, green, and blue spectral regions, in which subtractive dye images are formed, the combination of yellow i and magenta in equal amounts being too orange, said blue-sensitive emulsion being also sensitive to the red spectral region in an amount /10 to /100 of the blue light sensitivity.

5. The method of improving the rendition of red light in a photographic color process employing at least a blue-sensitive silver halide emulsion and a green-sensitive silver halide emulsion, which comprises sensitizing, the blue-sensitive silver halide emulsion to red light in an amount approximately lio to /ioo of its blue light sensitivity, exposing said emulsions to blue and green light, and forming a yellow dye image in said blue-sensitive emulsion, and a magenta image in said green-sensitive emulsion, the combination of the yellow and magenta in equal amounts being too orange in the absence of said red light sensitivity.

RALPH M. EVANS.

WESLEY T. HANSON, JR.- 

